Theorie:

Study the information about the structure: preposition (in/for/about) + -ing.
  
1. If a preposition is followed by a verb, the verb ends in -ing.

Are you interested in working for us?

How about meeting for lunch tomorrow?
  
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Mike must be fed up with studying.
 
2. Remember the use of these prepositions + -ing.

Before + -ing
After + -ing
By + -ing
Without + -ing

Before going out, she called Martin.

You can improve your Spanish by reading more.
  
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She has many problems without having to worry about yours.
 
Quellen:
worldartsme.com
www.howardandhowardevents.com
www.huffingtonpost.ca